Drill pipe having a journal formed thereon

ABSTRACT

A drill pipe ( 1; 12 ) has a journal ( 2; 15 ) formed thereon. Integrally formed stop collars ( 10, 11; 16, 17 ) are provided at each end of the journal ( 2; 15 ). The arrangement enables rotatable tools ( 18 ) to be fitted directly to a journal ( 2; 15 ) to reduce friction between the rotatable tool ( 18 ) and the journal ( 2; 15 ). The journal ( 2; 15 ) may be of a substantially greater length than the length of the rotatable tool ( 18 ) to facilitate lubrication and cooling. Alternatively removable stop collars ( 30; 31 ) are secured adjacent the ends of a journal ( 28 ) formed on the drill pipe ( 25 ). Methods of forming the journal surface ( 2; 15 ) during manufacture of a drill pipe are disclosed. There are also disclosed methods for reconditioning an existing drill pipe ( 20 ) to form a journal ( 21 ) thereon.

TECHNICAL FIELD

The present invention relates to a drill pipe, a method of forming drillpipe and drill pipe formed thereby as well as to a method ofreconditioning drill pipe formed by conventional methods.

BACKGROUND TO THE INVENTION

Some currently available torque and drag reducing tools used in drillingapplications installed directly onto drill pipes. Such tools may rotateabout the drill pipe to reduce rotational torque. As the outer surfaceof standard drill pipe is neither perfectly round nor smooth, such toolshave compromised torque reduction performance. Additionally, the fluidfilm operational principle of such tools sees drilling fluid, containingabrasive drill cuttings, passing between the tool and the drill pipe.This creates wear on the drill pipe and may compromise the strength ofthe drill pipe, particularly as the wear patterns can be deepcircumferential grooves which may act as stress raisers in the tubularwall.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a drill pipe having anintegrally formed journal area having improved hardness, roundness andsmoothness and methods of forming a journal on a drill pipe, or to atleast provide the public with a useful choice.

According to a first aspect of the invention there is provided a drillpipe having coupling sections at either end thereof:

a pair of stop collars integrally formed with the drill pipe andextending radially outward; and

wherein a hardfacing material has been applied to the outer surface ofthe drill pipe between the stop collars to form a journal for supportinga rotating tool.

According to a further aspect of the invention there is provided a setof drill pipes as hereinbefore described wherein the stop collars of thedrill pipes are located at different positions along the drill pipes tofacilitate efficient stacking of the drill pipes.

According to a further aspect of the invention there is provided acombination comprising a drill pipe as hereinbefore described and adrilling tool. The length of the journal is sufficiently longer than thelength of the drilling tool to facilitate lubrication and cooling of theinterface between the journal and the tool to reduce frictiontherebetween.

According to another aspect of the invention there is provided a methodof forming a journal on a drill pipe during manufacture comprising thesteps of:

i/ applying a hardfacing material to a section of the drill pipe betweena pair of intregally formed stop collars prior to heat treating thedrill pipe,

ii/ heat treating the drill pipe; and

iii/ precision grinding the section to which the hardfacing material hasbeen applied to form a smooth journal surface on the drill pipe.

The hardfacing is preferably an amorphous type hardfacing. Thehardfacing may be applied by high velocity oxy fuel, plasma spray,combustion powder, combustion wire, arc wire spraying, flame thermalspray, nitriding, carburising or other case hardening techniques.Alternatively, the hardfacing may be a ceramic material or PDC(polycrystalline diamond compact).

According to another aspect of the invention there is provided a methodof forming a journal on a section of preformed drill pipe comprising:

i/ lightly machining a section of the drill pipe between a pair ofintregrally formed stop collars;

ii/ applying a hardfacing material to the section of the drill pipe; and

iii/ grinding the hardfaced section so that it is round and smooth.

The hardfacing material is preferably applied by spluttering, forexample by twin arc or high velocity oxy fuel spraying the hardfacingmaterial directly onto the existing drill pipe. The hardfacing materialis preferably ARMORCOR M or ARNCO with options being Rolls Wood or othersuitable materials.

There is further provided a drill pipe having coupling sections ateither end thereof and a journal formed on the drill pipe between saidcoupling sections, the ovality of the journal being less than or equalto 0.7 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1a: shows a partial sectional side view of drill pipe with anintegrally formed journal surface;

FIG. 1b: shows a partial sectional side view of a drill pipe with adrilling tool secured thereto;

FIG. 1c: shows a partial sectional side view of a drill pipe havingseparate stop collars fitted thereto;

FIG. 2: shows a section of conventional drill pipe;

FIG. 3: shows the drill pipe of FIG. 2 after machining;

FIG. 4: shows the application of a hardfacing material to the drill pipeshown in FIG. 3;

FIG. 5: shows the drill pipe of FIG. 4 after grinding.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1a there is shown a drill pipe 1 having an integrallyformed journal generally indicated by the numeral 2. The drill stringhas a female coupling section 3 at one end, a mate coupling section 4 atthe other end and a pipe section 5 therebetween.

Female coupling 3 and male coupling 4 are preferably formed by forgingand are friction welded to respective ends of pipe section 5 at areas 6and 7. The thickness of the drill pipe is seen to vary gradually fromfemale coupling 3 and male coupling 4 to pipe section 5 at points 8 and9. This gradual tapering avoids the creation of a stress point at arapid transition.

Integrally formed collars 10 and 11 define a journal surface 12therebetween. The pipe string is formed substantially in accordance withstandard procedures apart from the procedures for forming journal 2.Female portion 3 and male portion 4 (including journal 2) are formed byforging and are friction welded to pipe section 5. Male fitting 4 isforged in a shape including collars 10 and 11 and journal surface 12.

Prior to heat treating the drill pipe in a standard forming procedure anamorphous type hardfacing material is applied to journal surface 12. Thehardfacing surface may be formed on journal surface 12 using casehardening techniques, such as nitriding or carburising. Alternativelyhigh velocity oxy fuel, plasma spray, combustion powder, combustionwire, arc wire spraying, or flame thermal spray techniques may be used.Alternatively, a ceramic layer or a PDC (polycrystalline diamondcompact) layer may be applied.

The drill pipe is then heat treated in the normal manner. The journalsurface 12 of the drill pipe so formed is then precision ground to forma smooth round journal surface upon which a tool may be fitted. Ascollars 10 and 11 are integrally formed during manufacture of the drillpipe 1 no additional collars need to be provided. Due to the smoothnessof journal 12 the problems associated with fitting tools directly todrill pipes encountered in the prior art may be substantially overcome.

Referring now to FIG. 1b there is shown a drill pipe 19 having male andfemale coupling sections 13 and 14 at either end thereof. Journal 15 islocated at a central region of the drill pipe 19 and stop collars 16 and17 are integrally formed with drill pipe 19 at either end of journal 15.A rotatable drilling tool 18 is secured about journal 15. A rotatabledrilling tool 18 may be a multi-part drilling tool as described in WO96/34173, or similar, which is able to be secured about journal 15 inuse.

The length b of journal 15 is preferably sufficiently greater than thelength a of rotatable drilling tool 18 to allow effective lubricationand cooling of the interface between journal 15 and rotatable drillingtool 18. Length b is preferably at least 20% greater than length a,preferably length b is more than 35% greater than length a, morepreferably length b is more than 50% greater than length a. By allowingthe rotatable drilling tool 18 to move along journal 15 lubricant may beintroduced to the interface between journal 15 and rotatable drillingtool 18 as well as allowing heat to dissipate from journal 15, thusreducing wear.

In the embodiment shown in FIG. 1b collars 16 and 17 are provided at acentral location along drill pipe 19. In the embodiment of FIG. 1a thestop collar 10 and stop collar formed by male coupling section 11 wereprovided at one end of the drill pipe 1. By providing a set of drillpipes having the collars located at different positions along the drillpipes the drill pipes may nestle together when stacked to achieve moreefficient stacking.

Referring now to FIG. 1c there is shown a drill pipe 25 having male andfemale coupling sections 26 and 27 at either end thereof. Journal 28 isformed on drill pipe 25 and a rotatable tool 29 is mounted upon journal28. In this case moveable stop collars 30 and 31 are secured at eitherend of journal 28. Stop collars 30 and 31 may be of two partconstruction so that they can be secured to drill pipe 25 in use. Thisarrangement allows the spacing between the stop collars to be varieddepending upon the tool secured to the drill pipe. It also simplifiesthe manufacture of drill pipe as the stop collars do not need to beintegrally formed, particularly for central areas of the drill pipe.This approach is also applicable where a journal is to be formed upon anexisting section of drill string.

The journals of the drill pipes described in FIGS. 1a to 1 c should beround, hard and smooth to minimise wear of the journal surface androtatable tool. The surface of the tool should have a roughness of lessthan 0.8 micrometers. The journal should have an ovality of less than orequal to 0.7 mm, preferably less than 0.5 mm and more preferably lessthan 0.25 mm. The journal should also have a surface hardness of greaterthan or equal to 35 Rc, preferably greater than 38 Rc. The length of thejournal will typically be less than 3 meters. Methods of forming thejournals will be described in conjunction with FIGS. 2 to 5 below.

When machining or treating preformed drill pipes care must be taken notto heat the drill pipe in such a manner that it loses its temper.Referring now to FIGS. 2 to 5 a method of reconditioning a drill pipe isshown schematically.

In FIG. 2 a drill pipe 20 is shown prior to reconditioning. In the firststep shown in FIG. 3 a section 21 of the drill pipe is lightly machined,preferably by rotating the drill pipe in a lathe relative to bit 22which moves along the section 21. The extent of machining has beengreatly exaggerated for illustrative purposes.

In the next step shown in FIG. 4 a hardfacing material is applied. Theprocedure used to form the hardfacing must not heat the drill pipe 20 insuch a manner as to affect its temper. One method is to apply materialby spluttering, preferably by twin arc or high velocity oxy fuelspraying hardfacing material 23 directly onto section 21 of the drillpipe. This technique requires careful preheating of the drill pipe to atemperature which is not so hot as to affect the temper of the pipe butnot so cold that the hardfacing will not be successfully applied. Thehardfacing material 23 is deposited using a finely calibrated arctransfer pressure. A back-step application technique may be required toensure that the base material temperature remains within acceptablelimits.

Preferred hardfacing materials are ARMORCOR M or ARNCO. It will,however, be appreciated that other suitable techniques or materials maybe employed as long as the above requirements are met.

In the final step, shown in FIG. 5, the hardfaced section 21 is groundby aluminium oxide grinder 24 so that the journal surface 21 is roundand smooth. A drilling tool may then be installed onto the drill pipe inthe normal way. If required, collars may be provided at either end ofjournal section 21.

The invention thus provides an improved drill pipe including anintegrally formed journal which enables rotatable tools to be directlymounted to the journal surface resulting in decreased friction betweenthe tool and the drill pipe and minimising wear on the drill pipe.

There is also provided a method of reconditioning existing drill pipe toprovide a journal for receiving a tool which results in reduced frictionbetween the tool and the drill pipe and minimises wear on the drill.

Where in the foregoing description reference has been made to integersor components having known equivalents then such equivalents are hereinincorporated as if individually set forth.

Although this invention has been described by way of example it is to beappreciated that improvements and/or modifications may be made theretowithout departing from the scope of the present invention as defined inthe claims.

What is claimed is:
 1. A drill pipe having coupling sections at eitherend thereof and a journal formed on the drill pipe between said couplingsections, wherein the journal has a surface hardness of greater than orequal to 35 Rc.
 2. A drill pipe as claimed in claim 1 wherein thejournal has an ovality that is less than 0.5 mm.
 3. A drill pipe asclaimed in claim 1 wherein the journal has an ovality that is less than0.25 mm.
 4. A drill pipe as claimed in claim 1, wherein stop collars areintegrally formed with the drill pipe.
 5. A drill pipe as claimed inclaim 1, wherein the journal has a surface hardness of greater than orequal to 38 Rc.
 6. A drill pipe having coupling sections at either endthereof and a journal formed on the drill pipe between said couplingsections, wherein the journal has an ovality that is less than or equalto 0.7 mm, and wherein the surface of the journal has a roughness ofless than 0.8 micrometers.
 7. A drill pipe having coupling sections ateither end thereof and a journal formed on the drill pipe between saidcoupling sections, wherein the journal has an ovality that is less thanor equal to 0.7 mm, and wherein the journal has a surface hardness ofgreater than or equal to 35 Rc.
 8. A drill pipe comprising: couplingsections at either end thereof; a journal formed on the drill pipebetween said coupling sections, the journal having an ovality that isless than or equal to 0.7 mm; and removable stop collars positionedadjacent each end of the journal on the drill pipe.
 9. A drill pipehaving: coupling sections at either end thereof; a pair of stop collarsintegrally formed with the drill pipe and extending radially outward;and wherein a surface of the pipe between the stop collars has aroughness of less than 0.8 micrometers to form a journal for supportinga rotating tool.
 10. A drill pipe comprising: coupling sections ateither end thereof; a pair of stop collars integrally formed with thedrill pipe and extending radially outward; a journal formed on the drillpipe between the stop collars, wherein the journal is configured toreceive a drilling tool of a given length disposed therearound such thatan interface is created between the journal and the drilling tool; andwherein the spacing between the pair of stop collars is greater than thelength of the drilling tool by an amount sufficient to promotelubrication and cooling of the interface between the tool and the drillpipe.
 11. A drill pipe having a first end and a second end, and an outersurface between the first end and the second end, the drill pipecomprising: a first coupling at the first end, the first coupling havingan enlarged diameter portion; a second coupling at the second end; apair of stop collars disposed on the drill pipe, the stop collarsextending radially outward to define an enlarged diameter on the outersurface of the drill pipe; and wherein a hardfacing material has beenapplied to the outer surface of the drill pipe between the stop collarsto form a journal for supporting a rotating tool.
 12. A drill pipe asclaimed in claim 11, wherein the pair of stop collars is integrallyformed with the drill pipe.
 13. A drill pipe as claimed in claim wherein12, the journal has an ovality that is less than or equal to 0.5 mm. 14.A drill pipe as claimed in claim 12, wherein the journal has an ovalitythat is less than or equal to 0.25 mm.
 15. A drill pipe as claimed inclaim 12, wherein the journal has a surface hardness of greater than orequal to 38 Rc.
 16. A drill pipe as claimed in claim 12, wherein thejournal is located in a central region of the drill pipe between thefirst and second couplings.
 17. A drill pipe as claimed in claim 12,wherein the surface of the journal has a roughness of less than 0.8micrometers.
 18. A drill pipe as claimed in claim 12, wherein thejournal has an ovality that is less than or equal to 0.7 mm.
 19. A drillpipe as claimed in claim 12, wherein the length of the journal is lessthan approximately 3 meters.
 20. A drill pipe as claimed in claim 12,wherein the journal has a surface hardness of greater than or equal to35 Rc.
 21. A drill pipe as claimed in claim 12, wherein: the journalreceives a drilling tool disposed therearound such that an interface iscreated between the journal and the drilling tool; and the pair of stopcollars are positioned so that for a drilling tool of a given length,the spacing between the pair of stop collars is greater than the lengthof the drilling tool by an amount sufficient to promote lubrication andcooling of the interface between the tool and the drill pipe.
 22. Adrill pipe as claimed in claim 21, wherein the spacing between the stopcollars is at least 20% greater than the length of the drilling tool.23. A drill pipe as claimed in claim 21 wherein the spacing between thestop collars is at least 50% greater than the length of the tool.
 24. Adrill pipe as claimed in claim 21, wherein the spacing between the pairof stop collars is at least 35% greater than the length of the drillingtool.
 25. A combination comprising a drill pipe as claimed in claim 12,and a drilling tool wherein the tool is securable about the journal ofthe drill pipe so that the journal is at least partially located withina bore in the drilling tool.
 26. A combination as claimed in claim 25wherein the spacing between the stop collars is at least 20% greaterthan the length of the tool.
 27. A combination as claimed in claim 25wherein the spacing between the stop collars is at least 35% greaterthan the length of the tool.
 28. A combination as claimed in claim 25wherein the spacing between the stop collars is at least 50% greaterthan the length of the tool.
 29. A set of drill pipes as claimed inclaim 12, wherein the stop collars of the drill pipes are located atdifferent axial positions along the drill pipes to facilitate efficientstacking of the drill pipes.
 30. A drill pipe as claimed in claim 11,wherein one of the pair of stop collars is the first coupling.